The present invention relates to a planar light source system using a substantially point-shaped light source such as an LED light source or the like used for a liquid crystal display device or the like, and particularly to a planar light source system which is used for mobile electronic equipment such as a cellular phone, a portable information terminal or personal digital assistant (PDA), an electronic organizer, a game machine, a note type personal computer or the like and is designed to be enhanced in miniaturization and reduced in power consumption, and a light deflecting device used therefor.
Demands for mobile electronic equipment such as a cellular phone, a portable information terminal or personal digital assistant, an electronic organizer, a game machine, a note type personal computer, etc. has been recently enhanced, and a light source which is reduced in power consumption and designed to have a thin body and also provides high and uniform luminance has been required as a back light source for a liquid crystal display device for such a mobile electronic equipment.
An under-lighting type in which plural linear light sources such as fluorescent lamps or the like are arranged in a housing or an edge-lighting type in which a linear light source is disposed at a side end surface of a planar light guide has been hitherto known as a back light source device used for a liquid crystal display device, a signboard, a traffic direction board or the like. With respect to the under-lighting type back light source, it is difficult to reduce the weight of the light source portion and also reduce the thickness of the light source portion, and also there occurs a see-through phenomenon that fluorescent lamps or the like used as a light source are seen through a display panel.
Therefore, the edge-lighting type has been more frequently used as a light and thin back light source device. Such an edge-lighting type light source device is a planar light source system as described below. That is, according to the planar light source system, a plate-shaped transparent material such as an acrylic resin plate or the like is usually used as a light guide, and a light source is disposed so as to confront the side end surface of the light guide. Light emitted from the light source is introduced into the light guide through the side end surface (light incident face) thereof, and the light thus introduced into the light guide is emitted in a planar shape from a light emission face of the light guide by using a light emission function such as a light diffusing portion formed on a front surface (light emission face) or back surface of the light guide. The light thus emitted by the light emission function is generally emitted in a slant direction to the emission face of the light guide, and thus it is general that an emission direction controller such as a prism sheet or the like is mounted on the light guide to deflect the light in the normal direction of the light emission face of the light guide.
For example, JP(A)-2-84618 or JP(U)-3-69174 has proposed a planar light source system in which a directional light emission structure such as a mat-finished surface or the like is formed on at least one of the light emission face of the light guide and the back surface thereof and a prism sheet having many linear elongated prisms arranged in parallel to each other is mounted on the light emission face. In such a planar light source system, the distribution of the emission light excessively expands, particularly in the vertical and parallel directions (more particularly, in the parallel direction) to the light source, and thus it does not sufficiently satisfy the requirements for low power consumption and high luminance.
Besides, from the viewpoint of reduction in power consumption and miniaturization, an LED light source is being used in a planar light source system for mobile electronic equipment or the like. Such a planar light source system using an LED light source is disclosed in JP(A)-9-81048 or JP(A)-9-152360. According to the disclosure of the former publication, an LED light source is disposed at the side end surface of a light guide, and one of the main surfaces of the light guide is set to a mat-finished surface while linear elongated prisms extending linearly are disposed on the other surface in parallel to the light incident edge. Further, according to the disclosure of the latter publication, an LED light source is disposed at the bottom surface side of a light guide having a prism shape on the back surface thereof, and light incident from the bottom surface is guided with use of a mirror.
According to these planar light source systems described above, light is directed in the normal direction of the emission face of the light guide by the action of the prism shape provided to the light guide. However, since the linear prism extending straightly is formed in parallel to the light incident edge, light emitted from the LED light source in a slant direction cannot be directed in the normal direction of the light emission face of the light guide, so that an area located in the slant direction is dark and thus luminance unevenness occurs.
Furthermore, JP(A)-7-320514 proposes that an LED light source is disposed at the corner portion of a light guide and a diffusing light guide is used, and JP(A)-8-184829 discloses that both the surfaces of a light guide are roughened. However, according to these planar light source systems, light is emitted in a slant direction to the light emission face, and thus the luminance is lowered in the normal direction which is an usual observation direction.
Still furthermore, JP(A)-11-232918 and JP(A)-11-329039 proposes that a diffusion pattern is formed on the back surface of a light guide so that it is disposed discretely and arcuately with respect to a point light source. However, it is impossible for the formation of such a diffusion pattern to efficiently emit light propagating through the light guide in the normal direction of the light emission face of the light guide, so that sufficient luminance cannot be achieved.
Still furthermore, JP(A)-11-167028 or JP(A)-2001-143512 proposes that many elongated prisms or V-shaped grooves are concentrically formed on the front surface or back surface of a light guide with a point light source positioned at the center in a planar light source system using the point light source. By forming such a concentric pattern on the light guide, light can be emitted uniformly over the overall light emission face of the light guide to thereby suppress occurrence of luminance unevenness. However, according to these planar light source system, emission light from the light guide is emitted directly or through a light diffusion film, and the distribution of emission light from the planar light source system has low directionality, so that a planar light source system having high luminance cannot be achieved.
Besides, there is also proposed a planar light source system comprising a light guide having a light diffusion pattern such as a dot pattern or the like printed on a light emission face thereof, a light diffusion film disposed on the light emission face of the light guide, and two prism sheets disposed on the light diffusion film, wherein each of the prism sheets has many linear elongated prisms arranged in parallel to each other, each elongated prism having a right-angled isosceles triangular section, and two prism sheets are arranged so that the elongated prisms thereof are perpendicular to one another. However, according to this planar light source system, it is difficult to efficiently emit directional light emitted from an LED light source in the normal direction, and also the distribution of emission light is excessively expanded, so that the luminance in the normal direction and the light utilization efficiency are lowered.
Therefore, an object of the present invention is to provide a planar light source system which is suitably used as a planar light source system using a substantially point-shaped light source such as an LED light source or the like for use in a liquid crystal display device for mobile electronic equipment such as a cellular phone, a portable information terminal or personal digital assistant, an electronic organizer, a game machine, a note type personal computer or the like, and low in power consumption, compact in size, excellent in light utilization efficiency, high in luminance and excellent in luminance uniformity, and a light deflection device used in the planar light source system.
That is, according to the present invention, there is provided a planar light source system comprising at least one primary light source of substantially point-shaped light source; a light guide having a light incident face on which light emitted from the primary light source is incident, guiding the incident light and having a light emission face from which the incident light is emitted; and a light deflecting device for controlling a direction of an emission light from the light guide, wherein the primary light source is disposed at a corner portion or an end surface of the light guide, and many substantially arc-shaped elongated lenses are formed in parallel to each other on at least one surface of the light deflecting device so as to surround the primary light source.
In an aspect of the present invention, the light deflecting device has a light incident surface which confronts the light guide, and the substantially arc-shaped elongated lenses are formed on at least the light incident surface. In an aspect of the present invention, each of the elongated lenses formed on the light deflecting device comprises an elongated prism having two prism faces, and light incident through at least one prism face is internally reflected and emitted from a light emission surface in a desired direction. In an aspect of the present invention, each elongated prism of the light deflecting device comprises two prism faces, one prism face being farther from the primary light source and another prism face being nearer to the primary light source, and an intersecting angle between the prism face farther from the primary light source and a reference plane of the light deflecting device is equal to 40 to 80 degrees.
In an aspect of the present invention, at least a part of at least one prism face constituting each elongated prism of the light deflecting device is designed to have a convex or concave curved-surface. In an aspect of the present invention, when there is assumed virtual elongated prisms arranged at the same pitch as an arrangement of the elongated prisms of the light deflecting device, each virtual elongated prism having a triangular cross section with an apex angle of xcex8, and peak light in an emission light distribution of light emitted from the light emission face of the light guide being incident through one prism face, internally reflected by the other prism face and then emitted from the light emission surface in a desired direction, at least one prism face constituting each elongated prism of the light deflecting device is designed to have a convex curved-surface with respect to a shape of each of the virtual elongated prism. In an aspect of the present invention, the apex angle xcex8 of the virtual elongated prisms is set so that the peak light is emitted within xc2x15 degrees relative to the normal direction of the light emission surface of the light deflecting device. In an aspect of the present invention, when there is assumed virtual elongated prisms arranged at the same pitch as an arrangement of the elongated prisms of the light deflecting device, each virtual elongated prism having a triangular cross section with an apex angle of xcex8, and peak light in an emission light distribution of light emitted from the light emission face of the light guide being incident through one prism face, internally reflected by the other prism face and then emitted from the light emission surface in a desired direction, at least one prism face constituting each elongated prism of the light deflecting device is designed to have a concave curved-surface with respect to a shape of each of the virtual elongated prism.
In an aspect of the present invention, the light deflecting device has elongated lenses formed on at least a light emission surface at the opposite side to a light incident surface confronting the light guide. In an aspect of the present invention, the light deflecting device refracts light incident through the light incident surface and emits the light from the light emission surface in a desired direction. In an aspect of the present invention, each elongated prism of the light deflecting device comprises two prism faces, one prism face being farther from the primary light source and another face being nearer to the primary light source, and an intersecting angle between the prism face farther from the primary light source and a reference plane of the light deflecting device is equal to 35 to 55 degrees while an intersecting angle between the prism face nearer to the primary light source and the reference plane of the light deflecting device is equal to 35 to 55 degrees.
In an aspect of the present invention, the light guide contains therein a structure having a refractive index different from that of the light guide. In an aspect of the present invention, the light guide has an uneven shape on at least one surface thereof. In an aspect of the present invention, an average slant angle of the uneven shape formed on the surface of the light guide is equal to 2 to 12 degrees. In an aspect of the present invention, the uneven shape formed on the surface of the light guide comprises many elongated lenses arranged in parallel to each other. In an aspect of the present invention, the many elongated lenses are disposed in a substantially arc-shaped arrangement so as to surround the primary light source. In an aspect of the present invention, the elongated lenses are discretely arranged with a flat portion interposed between neighboring elongated lenses. In an aspect of the present invention, a ratio of the lens portion to the flat portion is varied. In an aspect of the present invention, the ratio of the lens portion to the flat portion is increased as the distance from the primary light source is increased. In an aspect of the present invention, the ratio of the lens portion to the flat portion is varied in a circumferential direction of an arc shape surrounding the primary light source. In an aspect of the present invention, the uneven shape formed on the surface of the light guide is a roughened surface. In an aspect of the present invention, the light guide has uneven grooves on the opposite surface to the surface on which the uneven shape is formed so that the uneven grooves extend in a radial direction with the primary light source positioned substantially at the center.
According to the present invention, there is also provided a light deflecting device for a planar light source system, wherein the light deflecting device is designed in a rectangular shape and has many elongated lenses arranged in parallel to each other on at least one surface thereof, the elongated lenses extend substantially arcuately with a corner portion or one point of an end surface of the light deflecting device positioned substantially at the center of an arc.
In an aspect of the present invention, the elongated lenses are formed on at least a light incident surface thereof. In an aspect of the present invention, each of the elongated lenses comprises an elongated prism having two prism faces, and light incident through at least one prism face is internally reflected and emitted from a light emission surface in a desired direction. In an aspect of the present invention, each of the elongated prisms comprises two prism faces, one of which is located at a farther position from the center of the arc and the other of which is located at a nearer position to the center of the arc, and an intersecting angle between the prism face located at the farther position from the center of the arc and a reference plane of the light deflecting device is equal to 40 to 80 degrees.
In an aspect of the present invention, at least a part of at least one prism face constituting each of the elongated prisms is designed to have a convex or concave curved-surface shape. In an aspect of the present invention, when there is assumed virtual elongated prisms arranged at the same pitch as an arrangement of the longated prisms, each virtual elongated prism having a triangular cross section with an apex angle of xcex8, and peak light in a distribution of light incident through the light incident surface being incident on one prism face, internally reflected by the other prism face and then emitted from the light emission surface in a desired direction, at least one prism surface constituting each of the elongated prisms is designed to have a convex curved-surface with respect to a shape of each of the virtual elongated prism. In an aspect of the present invention, the apex angle xcex8 of the virtual elongated prisms is set so that the peak light is emitted within xc2x15 degrees relative to the normal direction of the light emission surface of the light deflecting device. In an aspect of the present invention, when there is assumed virtual elongated prisms arranged at the same pitch as an arrangement of the elongated prisms, each virtual elongated prism having a triangular cross section with an apex angle of xcex8, and peak light in a distribution of light incident through the light incident surface being incident on one prism face, internally reflected by the other prism face and then emitted from the light emission surface in a desired direction, at least one prism surface constituting each of the elongated prisms is designed to have a concave curved-surface with respect to a shape of each of the virtual elongated prism.
In an aspect of the present invention, the elongated lenses are formed on at least a light emission surface at the opposite side to a light incident surface. In an aspect of the present invention, light incident through the light incident surface is refracted and emitted in a desired direction from the light emission surface. In an aspect of the present invention, each of the elongated prisms comprises two prism faces, one prism face being farther from the center of the arc and the other face being nearer to the center of the arc, and an intersecting angle between the prism face farther from the center of the arc and a reference plane of the light deflecting device is equal to 35 to 55 degrees while an intersecting angle between the prism face nearer to the center of the arc and the reference plane of the light deflecting device is equal to 35 to 55 degrees.